var stream=require('stream');
var Readable=stream.Readable;
var util=require('util');

function MyReadable(){
    Readable.call(this);
}
util.inherits(MyReadable,Readable);
// for(var i in Readable.prototype){
//     MyReadable.prototype[i]=Readable.prototype[i];
// }
// MyReadable.prototype=Readable.prototype;

var rs=new MyReadable();
var c='a'.charCodeAt(0);
rs._read=function(){
    if(c<='z'.charCodeAt(0)){
        rs.push(String.fromCharCode(c++));
    }
    else{
        rs.push(null);
    }
}
rs.pipe(process.stdout);
